8086 Microprocessor
Microprocessor
Program controlled semiconductor device (IC) which fetches (frommemory), decodes and executes instructions.
It is used as CPU (Central Processing Unit) in computers.
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Microprocessor
First GenerationBetween 1971 – 1973
PMOS technology, non compatible with TTL4 bit processors 16 pins
8 and 16 bit processors 40 pinsDue to limitations of pins, signals are
multiplexed
Second GenerationDuring 1973NMOS technology Faster speed, Higher density, Compatible with TTL4 / 8/ 16 bit processors 40 pinsAbility to address large memory spaces and I/O portsGreater number of levels of subroutine nestingBetter interrupt handling capabilities
Intel 8085 (8 bit processor)
Third GenerationDuring 1978
HMOS technology Faster speed, Higher packing density
16 bit processors 40/ 48/ 64 pinsEasier to program
Dynamically relatable programsProcessor has multiply/ divide arithmetic
hardwareMore powerful interrupt handling
capabilitiesFlexible I/O port addressing
Intel 8086 (16 bit processor)
Fourth GenerationDuring 1980sLow power version of HMOS technology (HCMOS)32 bit processorsPhysical memory space 224 bytes = 16 MbVirtual memory space 240 bytes = 1 TbFloating point hardwareSupports increased number of addressing modes
Intel 80386
Fifth Generation Pentium
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Features:•It requires a single +5V supply•It is a 16 bit processor•It can access a memory of 1MB(2^20)•It can generate 16 bit I/O address hence it can access2^16=65536 I/O ports•It is possible to perform bit, byte, word and blockoperations•The Intel 8086 is designed to operate in two modesnamely minimum mode and maximum mode•The Intel 8086 supports multiprogramming•The words will be stored ion two memory locations.If the first byte of word is at an even address, the8086 will read the entire word in one operation.If the first byte of word is at odd address, the 8086will read the first byte in one operation and thesecond byte in another operation
Architecture of 8086
• The architecture of 8086 includes
– Arithmetic Logic Unit (ALU)
– Flags
– General registers
– Instruction byte queue
– Segment registers
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EU & BIU
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General Register
Control Register
Segment Register
CPU Register Set
Data Register
Index Register
Pointer Register
AH AL
BH BL
CH CL
DH DL
07815
Stack Pointer (SP)
Base Pointer (BP)
Source Index (SI)
Destination Index (DI)
Code Segment (CS)
Data Segment (DS)
Extra Segment (ES)
Stack Segment (SS)
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Registers OperationAX Word multiplication and division, word I/O
AL Byte multiplication and division, Byte I/O, Translation, Decimal Arithmetic Operations
AH Byte multiplication and division
BP Enter, Leave 80186 or 80286 onwards
BX Translation and Base register
CX String Operation and Counter
CL Variable shift and rotate
DX Word multiplication and division
SP Stack Operation
SI & DI String Operation
Functional blocksMicroprocessor
Flag Register
Timing and control unit
Register array or internal memory
Instruction decoding unit
PC/ IP
ALU
Control Bus Address Bus
Data Bus
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Computational Unit;performs arithmetic andlogic operations
Various conditions of the results are stored as
status bits called flags in flag register
Internal storage of data
Generates theaddress of theinstructions to befetched from thememory and sendthrough addressbus to thememory
Decodes instructions; sendsinformation to the timing andcontrol unit
Generates control signals forinternal and externaloperations of themicroprocessor
Overview 8086 Microprocessor
First 16- bit processor released byINTEL in the year 1978
Originally HMOS, now manufacturedusing HMOS III technique
Approximately 29, 000 transistors, 40pin DIP, 5V supply
Does not have internal clock; externalasymmetric clock source with 33%duty cycle
20-bit address to access memory canaddress up to 220 = 1 megabytes ofmemory space.
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Pins and signals
Pins and Signals8086 Microprocessor
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Common signals
AD0-AD15 (Bidirectional)
Address/Data bus
Low order address bus; these aremultiplexed with data.
When AD lines are used to transmitmemory address the symbol A is usedinstead of AD, for example A0-A15.
When data are transmitted over AD linesthe symbol D is used in place of AD, forexample D0-D7, D8-D15 or D0-D15.
A16/S3, A17/S4, A18/S5, A19/S6
High order address bus. These aremultiplexed with status signals